Metal treating bath and chelating agent for metal reactive acid baths



United States Patent 3,438,901 METAL TREATING BATH AND CHELATING AGENT FOR METAL REACTIVE ACID BATHS Neiko I. Vassileff, 12 E. 63rd St., New York, N.Y. 10021 No Drawing. Filed Oct. 22, 1965, Ser. No. 502,319 Int. Cl. (323g 1/06 US. Cl. 252-793 Claims ABSTRACT OF THE DISCLOSURE A new treating, pickling, etching, acid bath for metal is provided with a chelating agent reacting or acting catalytically to extend the useful life of the bath. The chelating agent for metal acid baths is also provided for its separate introduction into selected metal acid baths.

This invention relates generally as indicated to a metal treating bath and to a process for the treatment of metallic surfaces, and more particularly to such a treating bath and process in which a chelating control composition is used.

The metal treating processes of the type to which this invention generally relates are those in which the metal is subjected to treatment with an acid to remove either selected areas of a metallic surface or undesired foreign substances therefrom. Specifically, such treatments include etching processes, such as those used in photomechanical processes, and the well-known pickling process used in the manufacture of steel. In such processes, the metal is subjected to contact with the acid for a specified period of time under appropriate temperature conditions and acid concentrations to effect the desired treatment. In treating baths of this type, the solution will, after a relatively short period of time, become sufficiently saturated with the removed substances that it is necessary to discontinue use of the bath and to replace it with a new bath. Obviously, the expense of such procedure is objectionable, and it is accordingly extremely desirable to provide a treating bath which is capable of being used satisfactorily for a significantly extended period of time.

Accordingly, it is an object of the present invention to provide a metal treating bath and a process therefor in which the useful working life of the bath has been greatly extended.

It is another object of this invention to provide a treating bath which is considerably less expensive to use than those which have been heretofore employed.

Yet another object of this invention is to provide a metal treating bath which is capable of containing increased amounts of substances removed from the surface of metals without having its treating capabilities impaired appreciably.

An additional object of this invention is the provision of a metal treating bath in which the rate of reaction of the bath is significantly increased.

Other objects, features, and advantages of this invention will become apparent to those skilled in the art after a reading of the following more detailed description.

These and other objects are achieved by means of this invention in which a unique treating bath is provided which comprises generally an inorganic acid which may be any of those customarily used for the metal treatment and a chelating control composition which utilizes a combination of ingredients, specifically an alkali metal salt of an aliphatic polyhydroxy monocarboxylic acid, a hydroxy alkyl alkylene diamine polycarboxylate and a separate polyamine polycarboxylate derived from ethylene diamine tetra-acetic acid or ethylene triamine penta-acetic acid. It has been found that the three described ingredients of the chelating control composition interreact to provide a synergistic effect and thus exhibit a unique chelating control operable over a broad range of pH.

In general, the chelating control composition comprises in admixture:

(a) from about 5 to about weght parts of a metal salt of a saturated aliphatic polyhydroxy monocarboxylic acid;

(b) from about 5 to about 90 weight parts of a hydroxyl alkyl alkylene diamine polycarboxylate having the general formula:

wherein R is an alkylene group containing from 2 to 4 carbon atoms, R is an alkylene group containing from 1 to 5 carbon atoms, X is selected from the group consisting of -R'OH, and CH COOM, and M is selected from the group consisting of sodium, potassium, lithium, ammonium and substituted ammonium; and

(c) from about 5 to about 90 parts of a polyamine polycarboxylate selected from the group consisting of the alkali metal, ammonium and ferrous salts of ethylene diamine tetra-acetic acid and ethylene triamine pentaacetic acid,

the total of (a), (b) and (c) being parts by weight.

As explained previously, the metal treatment to which this invention relates is the type in which either selected areas or objectionable substances are removed from a metallic surface. In such a treatment, such as in pickling operations, the process occurring is the chemical removal of oxide scale from the iron or steel surface by the action of aqueous solutions of inorganic acids. Basically, the pickling reaction is between the soluble ferrous oxide and sulfuric acid or whatever acid is used. The ferrous oxide layer is the layer nearest the metallic surface and, depending on the manner in which the metal was previously treated, is normally covered by layers of magnetite (Fe O and ferric oxide of varying thicknesses. The supposition behind the success of the pickling operation is that the sulfuric acid reaches and reacts with the ferrous oxide layer through small cracks in the outer layers of scale and thus removes the scale from the surface.

In etching operations, essentially the same chemical process occurs although the reactants are different. In photomechanical processes, for example, such as in the production of lithographic plates, a metal plate, which may be aluminum, zinc, steel, chrome, copper, etc., with a film of light-sensitive material applied thereto is exposed to actinic light through a negative or stencil or the like so that certain portions of the light-sensitive material become light hardened. The plate is then developed to remove the unexposed or unhardened areas of the plate. The plate may then be etched with an etching solution, which is generally a dilute nitric acid solution, to remove the selected areas of the metallic surface. In such cases, a chemical reaction takes place between the metal and then acid to effect the removal of the surface.

In processes of this type, the removed materials very readily saturate the treating bath to a point where the bath contains an excess of such material and is thereafter ineffective for its intended treatment. According to the present invention, the bath life is increased quite substantially (as much as 50 to 100 percent more salts in baths of the same acid concentration and temperature) by addition of the aforedescribed chelating control composition thereto. The exact phenomenom which occurs due to such addition is not clearly known or understood, but it is believed that this composition reacts with the dissolved metal ions in the bath to form stable complexes, which are relatively chemically inert, and thus makes such chelated metals inert and accordingly unavailable for undesirable reactions and incapable of interfering with the desired chemical treatment which is occurring. The produced metal chelate is thus believed to have a catalytic action on the bath to increase the solubility product of the metal salts which accordingly reduces the interference of the saturated salt solutions with reaction of acid and metal at the interface.

In the case of the present invention, it has been found that if the temperature and acid concentration of the bath are maintained constant over a given period of time the addition of the described chelating composition increases the solubility of the metal salts in the acid bath without interfering with further solubilization of the metal. Because of the increased solubility product, the bath life is, of course, quite significantly increased.

One of the principal ingredients in the chelating metal control agent of this invention is a metal salt of an aliphatic polyhydroxy monocarboxylic acid. Any metal seems to be useful in this capacity, although for purposes of uniformity in relationship to the entire chelating metal control composition, it will be convenient for the metal to confer upon the salt solubility properties consistent with the solubility properties of the remaining ingredients. Thus, Where an aqueous medium is to be encountered in the ultilization of these materials, it will be found convenient to employ as the salt-forming ion an alkali metal, ammonia, or a substituted ammonia, for example, alkyl amines having the formula R-NH or R NH wherein R is an alkyl group containing from 1 to 3 carbon atoms. The alkali metals are well known and include sodium, potassium, lithium, cesium and rhubidium. Ammonia, of course, confers water-solubility upon the salt. The lower amines likewise confer Water-solubility on the end product, particularly because of the presence of more than one hydroxy group in the molecule. The salts which tend to be less water-soluble include the alkaline earth metal salts such as calcium, barium, strontium, magnesium, iron, cobalt, nickel, zinc, chromium, cadmium, manganese, zirconium, titanium, etc.

The aliphatic polyhydroxy monocarboxylates are conveniently derived from naturally occurring sugars and gums, such as, for example, by treatment of a sugar with HCN to form the nitrile followed by hydrolysis to form the monocarboxylic acid. These compounds are characterized by the presence therein of from 3 to 10 or more carbon atoms, at least two hydroxyl groups and most frequently one hydroxyl group attached to each carbon atom including the carboxyl carbon atom, and certain instances such as in the case of material derived from fructose, a carbonyl group intermediate the ends of the aliphatic chain. For most purposes these acids contain 5 or 6 carbon atoms and an equal number of hydroxyl groups including a hydroxyl group forming a part of the carboxyl group. The most notable examples of these materials include sodium gluconate, sodium glucoheptanate, potassium gluconate, ammonium gluconate, calcium gluconate, barium gluconate, zinc gluconate, sodium mannonate, potassium mannonate, sodium glycerate, potassium gluconate, the sodium, potassium, ammonium, and lithium salts of acids derived from natural gums such as Guar gum, locust bean gum, gum arabic, gum tragaucanth, etc. For most purposes, the alkali metal gluconates, and glucoheptanates, the ammonium gluconates and glucoheptanates, and the amine gluconates and glucoheptanates will be found suitable for use in the compositions intended for aqueous utilization in the processes of this invention, and the calcium, barium, magnesium gluconates and glucoheptanates will be found suitable for use in those procedures involving non-aqueous media.

The second principal component of the chelating metal control compositions useful in the present invention is, as

indicated above, a hydroxy alkyl alyklene diamine polycarboxylate having the general formula:

wherein R is an alkylene group containing from 2 to 4 carbon atoms, R is an alkylene group containing from 1 to 5 carbon atoms, X is a radical selected from the group consisting of -R'OH and CH -COOM, and M is selected from the group consisting of sodium, potassium, lithium, ammonium and substituted ammonium. A particularly suitable example for use as the second component of the chelating metal control composition of this invention is the sodium salt of hydroxy ethyl ethylenediamine tri-acetic acid. Also of particular utility in accord ance herewith is the di-hydroxy ethyl ethylene-diamine diacetate of sodium. As indicated above, the central alkylene group, R, may be ethylene, propylene, isopropylene, butylene, isobutylene, amylene, isoamylene, etc. The longer the alkylene groups these compositions, the greater solubility in non-aqueous media, such as mineral spirits. The alkaline earth metal salts, such as, the barium salts of hydroxy ethyl ethylene diamine triacetic acid may conveniently be used in the chelating metal control composition particularly adapted for non-aqueous emulsion polymerization media. Other salts suitable for use as component (b) of the present chelating metal control compositions include the sodium salts of hydroxy propyl, propylene diamine tri-acetic acid, the potassium salt of hydroxy butyl butylene diamine triacetic acid, the sodium salt of di-(hydroxy ethyl)propylene diamine di-acetic acid, the calcium salt of hydroxy ethyl ethylene diamine triacetic acid, the ammonium salt of hydroxy ethyl ethylene diamine tri-acetic acid, the ethylamine salt of hydroxy ethyl ethylene diamine tri-acetic acid, and similar compounds as will occur to those skilled in the art.

The third principal ingredient of the chelating metal control compositions of the present invention is, as indicated above, a metal salt of a polyamine polycarboxylate in which all of the amino hydrogens have been replaced by carboxyl-containing aliphatic radicals, particularly the methylene carboxyl radical. Specific examples of component (c) of the chelating metal control composition useful in this invention include, therefore the sodium, potassium, lithium, cesium and rhubidium metal salts, and ammonium and substituted ammonium salts and particularly the ferrous salts of ethylene diamine tetra-acetic acid and ethylene trimine penta-acetic acid. The ferrous salts are particularly useful in those compositions to be used in controlling chelating metals and emulsion copolymerization reactions between olefins and diolefins. In this event, it is unnecessary to add the iron as the ferrous sulphate or other water-soluble ferrous salt. Nitro-tri acetic acid salts may be used to replace part or all of this component, e.g. the sodium salt.

The chelating control compositions are conveniently employed as dry powders, although they may also, if desired, be employed in the form of aqueous solutions or pastes or as organic dispersions or solutions. The nature of the metal ions employed in neutralizing the acidic components will determine to a large extent the solvent system into which these materials are dissolved or dispersed.

In formulating the chelating metal control agents of the present invention, the relative proportions of compounds (a), (b) and (c) as above described are as follows:

Component (a), the metal salt of an alphatic polyhydroxy monocarboxylic acid is present in these compositions in an amount ranging from about 5 to about weight parts based on a total of parts by weight of components (a), (b) and (0).

Component (b), the hydroxyl alkyl alkylene diamine Example 1 Parts by weight Sodium gluconate 35 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 52 The sodium salt of ethylene diamine tetra-acetic acid 13 Example 2 Sodium gluconate 5 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid The sodium salt of ethylene diamine tetra-acetic acid 20 Example 3 Sodium gluconate The sodium salt of hydroxy ethyl ethylene diamine triacetic acid The solium salt of ethylene diamine tetra-acetic acid 75 Example 4 Sodium gluconate 27 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 40 The sodium salt of ethylene diamine tetra-acetic acid 33 Example 5 Sodium gluconate 12 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 17 The ferrous salt of ethylene diamine tetra-acetic acid 42 The sodium salt of ethylene diamine tetra-acetic acid 30 Example 6 Sodium gluconate 13 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 53 The sodium salt of ethylene diamine tetra-acetic acid 34 Example 7 Sodium gluconate 25 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 58 The sodium salt of ethylene diamine tetra-acetic acid 17 Example 8 Sodium glucoheptanate 90 The sodium salt of dihydroxy ethyl ethylene diamine diacetic acid 5 The sodium salt of ethylene diaminetetraacetic acid 5 Example 9 Sodium glucoheptanate 80 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 10 The sodium salt of ethylene diaminetetraacetic acid '10 Example 10 Ammonium gluconate 60 The ammonium salt of hydroxy propyl ethylene d1- amine triacetic acid 30 The ammonium salt of ethylene diaminetetraacetic acid 10 Example 11 Sodium glucoheptanate 80 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 10 The sodium salt of ethylene diaminetetraacetic acid 10 Trisodium phosphate 25 Example 12 Parts by weight Potassium glucoheptanate 5 The potassium salt of hydroxy butyl ethylene diamine triacetic acid The potassium salt of ethylene diaminetetraacetic acid 5 Example 13 Lithium glucoheptanate 5 The lithium salt of hydroxy ethyl ethyene diamine triacetic acid 5 The lithium salt of ethylene diamine tetraacetic acid 90 Example 14 Sodium glucoheptanate 80 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 10 The sodium salt of ethylene diaminetetraacetic acid 5 Sodium nitro triacetate 5 Example 15 Sodium gluconate 5 The sodium salt of hydroxyethyl ethylene diamine triacetic acid 80 The sodium salt of ethylene diamine tetra acetic acid 15 Sodium tripolyphos'phate 5 Example 16 Sodium glucoheptanate 72.7 The sodium salt of hydroxy ethyl ethylene diamine triacetic acid 18.2

The sodium salt of ethylene diamine tetraacetic acid 9.1

As indicated previously, the three ingredients of the chelating composition are operable over a wide range. For the particular treating process, it will, of course, be possible to determine the preferred percentages of the respective ingredients. In normal pickling or etching treating baths, the preferred ranges are from about 50 to Weight percent of component (a) and from about 5 to 20 Weight percent of each of components (b) and (c) based on the total Weight of the composition. Normally, the composition will be used in a quantity of from about 0.05 to 5.0 weight percent, based on the weight of the acid, although this quantity will also vary considerably depending upon the particular acid, its concentration, the treating temperatures, and the surface to be treated, as well as, of course, the type of treatment. Within the above-stated general range, the preferred range is from about 0.5 to 2.0 weight percent, based on the Weight of the acid.

In a typical pickling operation, sulfuric acid is the acid which is most generally used, and the acid concentration of the bath will normally vary within the range of from about 4 to about 20 percent by volume, depending upon the picklers type of operation. The preferred concentration of the bath will generally be between about 6 and 14 percent by volume. With sulfuric acid, commercial grade acid is preferably used and it is generally of a concentration of about 60 or 66 Baum. Other acids may also, of course, be used if desired, and these include nitric acid, hydrochloric acid, hydrofluoric acid and mixtures of such acids.

In general, the pickling operation is dependent upon numerous variables, such as the shape of the piece of metal being treated, the type of scale to be removed as well as the acid concentration and temperature. The speed of pickling is generally a function of the acid concentration, the bath temperature and the quantity of iron salts in solution. Obviously, as the acid concentration is lowered through use and the quantity of salts in the bath increases, the speed of pickling will begin to decrease and redeposition of dissolved salts will occur. Eventually, it will reach a point where speed and quality are no longer acceptable, as, for example, Where the bath contains 0.5 pounds of iron salts per gallon of pickling liquor, and it is then advisable to discard the bath and use a fresh 7 one. In general, the pickling temperature will normally be between about 140 and 180 F. although higher temperatures may be used if desired.

It is the standard practice in commercial pickling operations to include a commercially available corrosion inhibitor to provide a means of protection for the metal surface being treated. Corrosion inhibitors generally tend to slow down the action of the acid in the bath which causes the acid to confine most of its chemical action to the removal of scale. The use of such compounds has thus been found to increase significantly the iron loss during the pickling operation. Many such compounds are commercially available for this purpose and include starches, molasses, coal tar based substances, etc. More recently, the trend has been to the use of inhibitors comprising organic amine compounds such as ethylene diamine and long chain amines such as that sold under the trade name Duomeen T which is N-octadecyl 1,3-propylene diamine.

As is the standard practice in pickling, inhibitors of the above type may be employed in the present invention, although as will be demonstrated by the working examples which follow, the treating bath of this invention makes it possible to eliminate the use of inhibiting compounds. When an inhibitor is used, it is normally used in a quantity of about 0.5 to 1.0 weight percent based on the weight of the acid.

Anti-fume compounds may also be included as a part of the treating bath such compounds generally being detergent-type materials which produce foaming in the bath which in turn builds a protective layer or blanket on the surface thereof to keep the fumes in. Numerous such compounds are commercially available, and one particularly suitable such commercial compound for the present purposes is Foaming Compound No. 9 of Amchem Products, Inc. The anti-fume agent will normally be used in an amount of 0.1 to 1.0 weight percent based on the weight of the acid.

When the treating bath of this invention is to be used primarily for the etching of metallic surfaces, the inorganic acid used may be, of course, any of those commonly employed for such purpose. Normally, the acid will be a dilute solution of nitric acid, although other acids such as hydrochloric may be used as Well as the metal salts of such acids which are frequently employed such as for example a solution of ferric chloride.

It has become the common practice in etching, to include a film-forming agent as a part of the bath. Such film-forming agents provide a removable acid resistant film on the areas of the metal plate in which acid attack is undesirable, such as the side walls of the image areas thereof. Since the film-forming material will produce a film on these areas, the action of the nitric acid will be retarded somewhat and thus the dissolving action of the acid is controlled. The film-forming resins are normally formed from organic film-forming materials such as saturated aliphatic acids, e.g. valeric acid to cerotic acid in the homologous series of saturated aliphatic acids, esters of aliphatic acids and polyhydric alcohols such as Sorbitol laurate, diethylene glycol, monolaurate, etc., or wetting agents comprising an ester of sulfosuccinic acid and an aliphatic alcohol. For a thorough description and explanation of such agents in etching processes, reference may be made to US. Patents 2,640,763, 2,640,764 and 2,640, 765. It has also been proposed to use a petroleum sulfonate as for example a petroleum sulfonic acid or a salt of such acid as the film-forming agent, as well as materials such as dioctyl sulfosuccinate and dioctyl sodium sulfosuccinate. For a description of these materials, reference may be made to US. Patents 2,640,767 and 2,763,- 536.

Normally, the etching solution is a dilute aqueous solution of acid with an acid concentration of from about 2 to about percent by weight, with the particular concentration being dependent upon the type of surface to be etched.

This invention will be better understood by reference to the following specific but non-limiting examples.

Example 17 To demonstrate the improved results in the pickling of a steel surface, the treating bath of this invention was used in two standard pickling operations. The pickling medium was sulfuric acid, and the concentration of the bath varied in typical fashion throughout the duration of the pickling process as shown on the following chart. The temperature of the bath was maintained between about 160 F. and 180 F, with the average temperature being about 170 F. A commercially available inhibiting agent was also employed in the bath as per standard practice, and about 1 percent (by weight of acid) of the chelating composition of Example 9 was maintained in the bath. Periodic additions of acid, inhibiting agent and chelating composition were made as shown in the table.

The pickled steel had a clean, uniformly pickled surface and was also found to have a chemically clean surface with no indication of solubilized salts adhered thereto.

TABLE Addition 1 Percent Percent Run Time Temp., acid, iron,

(hrs.) Acid Ohel. Inhib. F. w wt.

Comp. percent percent 0 0. 5 1. 0 2.0 170 11.7 3.80 O 4. 0 12.0 10.0 170 11.1 0.40 9.5 0. 5 1. 0 2. 0 170 9.0 3. 9. 5 0. 5 1. 0 2.0 160 9. 4 1. 44 24.0 0. 5 1. 0 2.0 170 9. 5 6.00 24.0 0. 5 1. O 2.0 160 10. 2 1. 26. 5 0.75 1. 5 3.0 170 9. 2 5. 00 2G. 5 0. 5 1. 0 2.0 170 10.0 2. 00 33. 5 0. 5 1. 0 2. 0 170 9. 4 5. 20 33. 5 0. 5 1. 0 2.0 170 10. 1 2.50 50. 5 1. 0 2.0 4.0 167 9. 7 6.60 50. 5 O. 5 1. 0 2.0 170 10. 5 3. 02 57. 5 0. 5 1. 0 2. 0 170 10.0 6. 90 57. 5 0. 5 1. 0 2. 0 170 9. 4 3. 54 72. 0 0. 5 1. 0 2.0 170 10. 0 7. O0 72. 0 0. 5 1. 0 2.0 170 10. 3 3. 80 74. 9. 6 7. 20 74. 5 9. 4 4. 00 81. 5 0.75 1. 5 3.0 170 8. 6 8. 60 81. 5 0.75 1. 5 3.0 170 9. 1 4. 40 96.0 0. 5 1. 0 2.0 170 9. 6 9. 40 0. 5 1 0 2.0 160 11. 4 5.00 180 9. 0 9. 90

1 Acid addition is in tank units, chelating composition and inhibitor are in gallons.

2 Run 1 was discontinued for repair to the tank.

Analysis of the results set forth in the table shows that in Run No. 1, the bath had an iron concentration of about 9.90 percent when the run had to be discontinued due to necessary repairs of the tank, whereas in Run 2, the final iron concentration prior to dumping of the bath was 16.40 percent. When it is considered that a pickling bath is normally dumped when the iron con- .tent reaches a maximum of 4 or 5 percent, the results of these experiments clearly demonstrate the significant improvement emanating from this invention, as the results of Run No. 2 represent about a five-fold increase in the quantity of iron in the bath prior to discontinuation of the run. Moreover, the useful life of the bath has been greatly extended, the bath functioning satisfactorily for close to two weeks of pickling which is in contrast to the normal three to four days.

- Example 18 In this run, a sheet of billet wire grade R22 was pickled in a continuous strip pickler with sulfuric acid, at

a bath concentration of approximately 20 percent. The bath temperature was maintained at about 210 F. and was agitated with a magnetic stirring bar operating at about 420 rpm. Approximately 2 weight percent of the chelating control composition of Example 9 was used in the treating bath, based on the weight of the acid. The scale to be removed from the steel surface was principally mill scale.

30 minutes after descaling, the metal loss was approximately l.350 grams (about 0.496 percent). At the end of 60 minutes, the metal loss was 2.5721 grams or about 0.950 percent.

The results of the above test were compared with those achievable by the use of a commercial corrosion in hibitor. This produced a metal loss of 0.09 percent 30 minutes after descaling and 0.15 percent in 60 minutes after descaling. The brightness of the material after descaling was determined to be 28.1 percent, Whereas the brightness of steel pickled without such agent was in the range of 20 to 22 percent, as measured with a standard refiectometer to determine the increased reflection of the pickled steel.

Example 19 The procedure of the preceding example was followed except that the acid medium was hydrochloric and the treating bath had an acid concentration of about 10 percent. The temperature of the bath was maintained at 170 F. and 2.0 weight percent of the chelating control composition of Example 9, based on the weight of the acid, was used. The metal loss 30 minutes after descaling was 0.138 gram or 0.50 percent. 60 minutes after descaling, the metal loss was 0.2588 gram (0.93 percent).

These results were compared with tests utilizing only a commercial additive as in the preceding example without the chelating composition which had a metal loss of 0.09 for 30 minutes after descaling and 0.13 for 60 minutes after descaling. The brightness after descaling was determined to be 32.1 percent, whereas a similar sample pickled without the chelating control composition was 27.0 percent.

Further pickling tests of the same nature as those set forth above were also conducted, and it was found that the production rate with the treating bath of this invention was subsantially greater than normal on a given 8-hour working shift, being 124 tons per hour as opposed to the customary 75 tons per hour. Moreover, such tests demonstrated that the quantity of corrosion inhibitor used could be significantly reduced and in some instances completely eliminated and satisfactory results in quality of product and speed of pickling still achieved. Since corrosion inhibitors hinder pickling, it is thus desirable to eliminate their use, and also, of course, the additional ingredient increases the cost of operating the process. In one particular test, a 6500 gallon pickling bath containing 550 gallons of sulfuric acid and 11 gallons of the chelating composition of Example 9 without any corrosion inhibitor was used in a standard pickling process. This bath was used satisfactorily for 17 turns (one turn equals an eight-hour period of operation) whereas the normal life of a similar pickling bath without the chelating composition of this invention lasted only 6 turns. Also, the bath was used eifectively until the iron content was 11.8 percent.

The use of the chelating composition has also made it possible to decrease the quantity of acid necessary for satisfactory results. In some cases, the quantity of acid has been reduced by as much as 60 percent. The chelating composition of this invention is thus a significant contribution to the art of pickling.

Example 20 A clean, de-scummed plate of ground and polished zinc of standard thickness, which had been coated with a photosensitive diazo resin and exposed through a pattern, was etched with a dilute nitric acid solution containing approximately 2.0 percent of the chelating control composition of Example 9. This solution was continuously impinged against the surface of the plate by the commercial paddletype Dow etching machine which was used. It was found that at the end of the etching operation, the plate had improved quality as it was exceptionally clean and pimplefree with the shoulders noticeably tighter than normal. Additionally, the useful bath life was extended by approximately 60 percent in zinc content.

The above-described etching procedure was also used on a copper surfaced plate and comparable results were obtained.

- It is thus seen that the objects of this invention have been achieved by the provision of a metal treating bath containing the described chelating control composition. Such bath has been found to have increased solubility of salts but the chelating composition does not interfere with further solubilization and thus increases the bath life quite significantly as well as increasing the speed of treatment. Moreover, the quality of the finished product has been found to be an improvement over comparable metal objects treated in accordance with the heretofore known processes.

I, therefore, particularly point out and distinctly claim as my invention:

1. A metal treating bath for the removal of substances from metal surfaces consisting of an inorganic metal reactive acid capable of effecting such removal and a chelating control composition consisting of in admixture:

(a) from about 5 to about weight parts of a metal salt of a saturated straight chain hydrocarbon polyhydroxy monocarboxylic acid;

(b) from about 5 to about 90 weight parts of a hydroxyl alkyl alkylene diamine polycarboxylate having the general formula:

wherein R is an alkylene group containing from 2 to 4 carbon atoms, R is an alkylene group containing from 1 to 5 carbon atoms, X is selected from the group consisting of --R--OH, and -CH COOM, and M is selected from the group consisting of sodium, potassium, lithium and ammonium; and

(c) from about 5 to about 90 parts of a polyamine polycarboxylate selected from the group consisting of the alkali metal, ammonium and ferrous salts of ethylene diamine tetra-acetic acid and ethylene triamine penta-acetic acid,

the total of (a) (b) and (c) being 100 parts by weight, said chelating control composition being from about 0.05 to 5.0 percent, based on the weight of said acid.

2. The treating bath of claim 1 in which component (a) of said chelating composition comprises 50 to weight parts of said composition, and components (b) and (0) each comprise 5 to 20 weight parts, based on the total weight of the composition.

3. The treating bath of claim 1 in which 0.5 to about 2.0 weight percent, based on the weight of said acid of said chelating composition is used.

4. The treating bath of claim 1 in which said inorganic acid is selected from the group consisting of sulfuric acid, hydrochloric acid, hydrofluoric acid, nitric acid and mixtures thereof.

5. The treating bath of claim 1 in which component (a) of said chelating composition comprises about 50 to 95 weight percent of said chelating composition and components (b) and (0) each comprise about 5 to 20 weight percent of the total weight of said composition.

6. The treating bath of claim 1 in which component (a) is the sodium salt of such straight chain hydrocarbon polyhydroxy monocarboxylic acid, component (b) is the tri 1 1 sodium salt of hydroxyethyl ethylene diamine triacetic acid, and component (c) is sodium ethylene diamine tetraacetic acid.

7. A metal pickling bath consisting of an inorganic metal reactive acid capable of removing scale deposits from the surface of iron and steel and a chelating control composition consisting of in admixture:

(a) from about 5 to about 90 weight parts of a metal salt of a saturated straight chain hydrocarbon polyhydroxy monocarboxylic acid;

(b) from about 5 to about 90 weight parts of a hydroxyl alkyl alkylene diamine polycarboxylate having the general formula:

wherein R is an alkylene group containing from 2 to 4 carbon atoms, R is an alkylene group containing from 1 to 5 carbon atoms, X is selected from the group consisting of --R'OH, and -CH COOM, and M is selected from the group consisting of sodium, potassium, lithium and ammonium; and

(c) from about 5 to about 90 parts of apolyamine polycarborboxylate selected from the group consisting of the alkali metal, ammonium and ferrous salts of ethylene diamine tetra-acetic acid and ethylene triamine pentaacetic acid,

the total of (a), (b) and being 100 parts by weight, said chelating control composition being from about 0.05 to 5.0 percent, based on the weight of said acid, and said bath having an acid concentration of about 4 to 20 percent by volume.

8. A metal etching bath for the etching of metallic surfaces consisting of an etching medium consisting of inorganic metal reactive acids and a chelating control composition consisting of in admixture:

(a) from about to about 90 weight parts of a salt of a saturated straight chain hydrocarbon polyhydroxy monocarboxylic acid;

(b) from about 5 to 90 weight parts of a hydroxyl alkyl alkylene diamine polycarboxylate having the general formula:

wherein R is an alkylene group containing from 2 to 4 carbon atoms, R is an alkylene group containing from 1 to 5 carbon atoms, X is selected from the group consisting of ROH, and CH COOM, and M is selected from the group consisting of sodium, potassium, lithium and ammonium; and

(c) from about 5 to about parts of a polyamine polycarboxylate selected from the group consisting of the alkali metal, ammonium and ferrous salts of ethylene diamine tetra-acetic acid and ethylene triamine penta-acetic acid,

the total of (a), (b) and (c) being 100 parts by weight, said chelating control composition being from about 0.05 to 5.0 percent based upon the Weight of said acid, and said bath having an acid concentration of about 2 to 15 percent by Weight.

9. The etching bath of claim 8 in which said chelating control composition comprises about 0.5 to 2.0 weight percent of the Weight of said acid.

10. The etching bath of claim 8 in which component (a) of said chelating control composition comprises about 50 to weight percent of said composition and components (b) and (0) each comprises about 5 to 20 weight percent of the total Weight of said composition.

References Cited UNITED STATES PATENTS 2,396,938 3/ 1946 Bersworth '1342 2,687,346 8/ 1954 McDonald 252'79.3

FOREIGN PATENTS 818,151 8/1959 Great Britain.

852,958 11/1960 Great Britain.

MAYER WEINBLA'IT, Primary Examiner.

US. Cl. X.R. 

